Autologous transplantation of mobilized peripheral blood CD34⁺ cells selected by immunomagnetic procedures in patients with multiple myeloma

In the use of autologous PBPC transplantation in patients with multiple myeloma, contamination of PBPC with myeloma cells is commonly observed. Enrichment for CD34⁺ cells has been employed as a method of reducing this contamination. In this study the reduction of myeloma cells in PBPC was accomplished by the positive selection of CD34⁺ cells using immunomagnetic bead separation (Isolex 300 system). PBPC were mobilized from 18 patients using cyclophosphamide (4.5 g/m²) and G-CSF (10 μg/kg/day). A median of two leukaphereses and one selection was performed per patient. The median number of mononuclear cells processed was 3.50 x 10¹⁰ with a recovery of 1.11 x 10⁸ cells after selection. The median recovery of CD34⁺ cells was 48% (range 17-78) and purity was 90% (29-99). The median log depletion of CD19⁺ cells was 3.0. IgH rearrangement, assessed by PCR, was undetectable in 13 of 24 evaluable CD34⁺ enriched products. Patients received 200 mg/m² of melphalan followed by the infusion of a median of 2.91 x 10⁶/kg CD34⁺ cells (1.00-16.30). The median time to absolute neutrophil count > 0.5 x 10⁹/l was 11 days, and sustained platelet recovery of > 20 x 10⁹/l was 14 days. We conclude that immunomagnetic-based enrichment of CD34⁺ cells results in a marked reduction in myeloma cells without affecting engraftment kinetics.